Chronic immunosuppression is associated with infection, neoplasms, drug toxicity, metabolic effects and failure to control rejection. A non-toxic, easily applied method to induce tolerance is a goal of clinical transplantation. We produced stable tolerance and macrochimerism using anti-lymphocyte serum (ALS), rapamycin and donor bone marrow (BM) in fully major histocompatability complex (MHC) mismatched rodents. ALS and rapamycin is an extremely effective immuno-suppressive combination; ALS induces tissue lymphocyte depletion and T cell apoptosis while rapamycin promotes activation-induced T cell apoptosis. We seek to demonstrate the effectiveness of this protocol in cynomolgus monkeys prior to clinical application. In Aim 1, recipient monkeys will receive Thymoglobulin (day -1 to 10), rapamycin (day 0 to 90), renal allografts (day 0), with or without donor specific BM on day 10. Recipients will be followed by standard renal function tests and protocol biopsies and monitored serially for antidonor alloreactivity. Tissue lymphocyte depletion will be determined by histology, FACS analysis, T cell apoptosis and immune reactivity. Peripheral blood will be assayed for chimerism. Anti-donor immunity will be assayed by trans vivo DTH assays. Induction and stability of tolerance will be correlated with alterations in immune reactivity, degree and duration of chimerism, and extent of lymphocyte depletion. In addition, higher doses of BM and/or thymoglobulin, and cytokine (G-CSF) stimulated peripheral blood buffy coat cells will be tested for effectiveness in tolerance induction. Aim 2 will use RT -PCR and immunohistochemistry to identify anti-apoptotic genes A20, HO-l and Eck and correlate their presence with tolerance. Aim 3 will utilize real time RT -PCR to identify expression of various immune related genes as markers for subclinical rejection and gene chip analysis to identify patterns of gene expression associated with tolerance. This non-radiation based protocol employs two widely used agents, thymoglobulin and rapamycin, in combination with BM, as an easily applied, potentially well tolerated protocol for clinical tolerance induction.